The attached patch implements a convenience function
called getpeercred() which internally calls
getsockopt(SO_PEERCRED) to retrieve the credentials
(pid, uid and gid) of the remote process a socket is
attached to, in case the remote end is local.

This currently (AFAIK) only works (properly) on Linux
2.4+, but might work on BSD-style systems too.

The returned data is wrapped in a new ucred type, which
is subclassable to implement additional convenience
functions in Lib/socket.py.

The patch updates the socket module, the test suite,
the documentation (including whatsnew), and adds a
configure check for the definition of struct ucred in
sys/socket.h, which is the default place for struct
ucred if it is available.

If struct ucred is not available on the current system,
getpeercred() is made a dummy method, which returns a
python-defined ucred type which contains pid=0,
uid=gid=-1, which are the default values returned under
Linux when the call fails because there is no
credentials data associated with the socket.

The decision to move the data to a separate type was
made with respect to the ability to use struct ucred
under other systems in a SCM_CREDENTIALS sendmsg()
call. I'll post the implementation of sendmsg() and
recvmsg() as a separate tracker item, but the latter
patch will rely on the inclusion of this patch.

I'm uncomfortable with including something that only works on certain versions of a single platform. Are there any other functions or methods (not modules) that are only available for Linux? I can think of a number of places flagged as "Availability: Unix", but if getpeercred() doesn't work on the BSDs, it doesn't even meet that standard.

If a decision is made to include this, and if it only works on Linux 2.4+, I'd rather see it not available at all on other platforms (rather than returning dummy values).

Heiko, are you still interested given msg50314?

No reply to msg111039, also see comments on msg50314.